Power steering fluid reservoir

ABSTRACT

A reservoir for power steering fluid includes an upright housing that forms an upper interior space for storage of a reserve fluid supply, and a lower interior space containing a fluid filter. Fluid connectors are provided for causing fluid to flow in a circumferential swirling pattern as it moves through the filter, such that the flowing fluid has a relatively long residence time in the lower portion of the reservoir for achievement of an effective cooling action. The fluid filter is connected in a return line form the power steering unit to the associated pump, so that the filter exerts a back pressure on fluid flowing from the power steering unit to the filter.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a power steering fluid system for anautomobile vehicle, and particularly to a fluid reservoir for a powersteering fluid system. The reservoir incorporates a filtration unit thatis functionally located in the fluid return line from the power steeringunit to the fluid pump that supplies pressurized fluid to the powersteering unit.

A typical power steering system for a motor vehicle includes a fluidpump for supplying pressurized fluid to a power steering unit that isconnected to a return line that leads back to the pump. Often the fluidsystem includes a filter for trapping solid contaminants that can formduring prolonged usage of the power steering system. The filter can belocated in the pressure line between the pump and steering unit, or inthe return line between the steering unit and the pump. In manynon-sealed systems a reservoir is provided for supplying steering fluidto the system, and for accommodating excess fluid volumes associatedwith high fluid temperatures that occur in high temperature environmentsand/or cyclic operation of the power steering unit.

The present invention relates to a fluid reservoir for power steeringfluid, wherein the reservoir, which incorporates a filter, isfunctionally located in the return line between the power steering unitand the fluid pump. The reservoir is designed so that the fluid flowingthrough the filter is in a swirling condition, whereby heated fluid ismixed with relatively cool fluid so as to achieve a reasonably evenfluid temperature, without hot spots as might degrade the fluid or causefluid foaming.

A particular aim of the invention is to provide a reservoir having arelatively small height dimension, whereby the reservoir can fit withinsmall spaces in the vehicle engine compartment. Typically, the reservoirheight dimension can be in the neighborhood of six inches.

Patents of prior art interest are U.S. Pat. No. 5,906,221 to M. Mancell,U.S Pat. No. 5,820,356 to D. Ogbuaku, U.S. Pat. No. 4,650,572 to W.Hayes, and U.S. Pat. No. 5,918,760 to S. Frodin. The fluid reservoir ofthe present invention is advantageous over the prior art as regardscompactness, good fluid mixing cavitation prevention, and low noiseproduction. Circumferential swirling motion of the fluid is controlledto prevent cavitation of the swirling fluid mass, as might produceundesired noise. The filter is designed to exert a back pressure in thefluid return line, so as to minimize pulsations or flow variations thatmight generate a perceptible shudder or vibration during operation ofpower steering unit.

Further features of the invention will be apparent from the attacheddrawings and description of an illustrative embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view taken through a fluid reservoir embodying theinvention.

FIG. 2 is a transverse sectional view taken on line 2—2 in FIG. 1.

FIG. 3 is a section view taken in the same direction as FIG. 1, butillustrating another form that the invention can take.

FIG. 4 is a transverse sectional view on a reduced scale, taken on line4—4 in FIG. 3.

FIG. 5 is a fragmentary view showing a structural detail that can beemployed in practice of the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Referring to FIGS. 1 and 2, there is shown some features of a fluidreservoir embodying the invention. As schematically shown, fluidreservoir 10 is in circuit with a fluid pump 12 and power steering unit14 of conventional design. The fluid circuit includes a high pressureline 16 for supplying fluid to power steering unit 14, and a return line18 for returning depressurized fluid from the steering unit to pump 12.Reservoir 10 includes a filtration means 20 that is located in returnline 18 for trapping contaminants that can accumulate in the fluidsystem. The present invention is concerned primarily with theconstruction of the reservoir and associated filtration unit 20.

The illustrated reservoir includes an upright housing 22 formed by anupper housing section 24 and lower housing section 26. The two housingsection have mating flanges 28 that are secured together by anyconventional means, e.g. bolts, clamps, weld, etc. The two piece housinghas a circular plan configuration centered on a central vertical axis30.

Upper housing section 24 includes a filler tube 32 that is normallyclosed by a removable cap 34, such that replenishment fluid can be addedto the system, e.g. when the fluid level in the reservoir interior space35 falls below a desired level, designated by numeral 36 in FIG. 1. Anair vent opening 37 is provided in filler tube 32, or cap 34, tomaintain space 35 at a desired pressure.

The side wall 38 of upper housing section is preferably circular in theplan dimension. As shown in FIG. 1, the lower portion of wall 38 is anaxial continuation of a circular side wall 39 formed by the lowerhousing section 26.

The lower housing section 26 has a circular side wall having a steppedconstruction that includes a relatively large diameter circular sidewall 39 and a relatively small diameter circular side wall 42 joined towall 39 so as to form an upwardly facing internal ledge 44.

Upper housing section 24 serves as a fluid storage device for thereserve fluid supply required to keep the system in a filled condition.Excess fluid volumes associated with thermal fluid expansion can beaccommodated by interior space 35 formed by housing section 24. Underlow ambient temperature conditions, fluid can be supplied from interiorspace 35 to the system. The fluid in space 35 is usually relativelystatic (non-moving).

Lower housing section 26 serves as a fluid housing for filtration means20. The filtration means is a self-contained filtration unit that can beinstalled within housing section 26 as a unitary structure. Thefiltration unit includes an upright hollow circular frame 40 having alower annular edge 41 and upper annular edge 43. Rectangular window-likeopenings 45 are formed around the peripheral surface of the frame forpassage of fluid into the central space 47 defined by the frame. Afiltration media 49 having a minimum porosity of about forty microns issuitably supported on the outer surface of the circular frame, wherebyminute solid particles are trapped on, or near, the outer surface of thefiltration media.

Fluid is supplied to the filtration unit through a tubular inlet 50 thathas a tangent connection with circular side wall 39, such that theincoming fluid flows along the interior surface of circular side wall 39in a circumferential path concentric around the central vertical axis30. Annular space 52 surrounding the filtration unit is fluid-filled.

Filtration media 49 offers sufficient resistance to fluid flow as togenerate a back pressure on the fluid flowing from power steering unit14 into the filtration unit. The swirling fluid in annular space 52tends to climb up along the inner surface of circular wall 39 and thealigned surface of circular wall 38. The climbing action is controlled(or limited) by an annular frusto-conical partition 53 extendingoutwardly from upper annular edge 43 of the filtration frame 40.Partition 53 acts as a baffle or fluid containment wall. A row of ventports 55 is formed along the upper edge of partition 53, wherebyentrained air in the circumferentially-flowing stream is vented throughports 55 upwardly into the interior space 35. Boundary layer effects atthe joint between partition 53 and the side wall 38 of the upperreservoir section tend to stagnate or slow the swirling fluid to enhancethe de-aeration action. Ports 55 are preferably located at, or near, thehighest point in annular space 52, which tends to concentrated the airnear the ports.

Ports 55 are relatively small to minimize the flow of liquid through theports. The major percentage of liquid supplied to annular space 52travels through filtration media 49, not the vent ports 55. However,some liquid flow through the ports is not necessarily disadvantageous,in that heated liquid flowing upwardly through the ports mixes with therelatively cool liquid in space 35, thereby reducing the averagetemperature in the reservoir. Liquid flow through ports 55 may help toentrain air bubbles located on the undersurface of partition 53 near theports.

Filtration unit 20 is installed so that the lower annular edge 41 of thefiltration unit seats on internal ledge 44. The upper edge offrusto-conical partition 53 fits against an overlying ledge formed onthe housing side wall 38 to stabilized the filtration unit in thereservoir.

Fluid is discharged from the lower housing section 26 through a tubularoutlet 57 that is tangent to circular side wall 42. Pump 12 provides theimpetus for fluid flow through filtration unit 20. A suction forcegenerated by the pump is applied through tubular outlet 57 to the fluidin central space 47 to produce a swirling motion in space 47. Thetangential orientation of outlet 57 is a causative factor. Thetangential orientation of tubular inlet 50 produces a circumferentialswirling motion in annular space 52, such that the fluid flowing frominlet 50 to outlet 57 has an essentially continuous circumferential flowpattern around vertical axis 30.

Circumferential fluid flow through the reservoir is advantageous in thatthe fluid residence time is increased, so as to promote an extensivecooling action of the heated fluid introduced through inlet 50.

It will be noted that central space 47 within the filtration unit 20 isin open communication with interior space 35 defined by housing section24. This is advantageous in that fluid in space 35 can flow downwardlyinto space 47 to prevent cavitation in space 47. Especially at lowambient temperatures, the fluid in annular space 52 surrounding thefiltration unit may be relatively viscous so that inertia effects delaythe flow from space 52 across the filtration unit 20 into central space47.

Under such circumstances the pump suction might tend to producecavitation in space 47. However, fluid in the upper storage space 35 canreadily flow into space 47 to prevent such cavitation. Cavitation isdetrimental for several reasons, including the fact that it produces anannoying audible sucking noise.

The illustrated reservoir construction achieves filtration of the fluidflowing from power steering unit 14 to pump 12 while at the same timeprolonging the fluid residence time in the reservoir to promote adesired cooling action on the heated fluid. The relation between fluidstorage space 35 and central space 47 prevents cavitation in space 47,especially during pump start-up.

Filtration media 49 preferably has a relatively small size porosity, inthe neighborhood of forty microns. This enables the media to traprelatively small size contaminants. Also, the media is able to exert aback pressure on fluid flowing from power steering unit 14 towardtubular inlet 50. Such a back pressure tends to minimize fluid pulsationassociated with operation of the pump and steering unit. Such pulsationsare perceived by the vehicle occupants as a vibration or shudder in thesystem. The use of a forty micron filtration media tends to reduce suchshudder, due to the back pressure produced by the filtration media.

The reservoir shown in FIG. 1 has a height dimension that isapproximately the same as the diametrical dimension. Each dimension canbe about six inch. With such proportioning the reservoir can fit intosmall clearance spaces that would not accommodate a taller unit, whilestill providing access to cap 34 and filler tube 32. The relativelylarge diameter filtration unit 20 can have a reasonably large filtrationmedia surface area without unduly increasing the height of thefiltration unit.

FIG. 5 of the drawings illustrates a fluid connection that can be usedas an alternate for the tangential fluid connections 50 and 57. The FIG.5 fluid connection includes a cylindrical tubular section 59 extendingoutwardly from the housing side wall along a radius from axis 30, and acircumferentially extending section 61 located within the housing.Hollow section 61 causes the fluid to move circumferentially as itenters (or leaves) the connector. FIG. 5 is illustrative of variousmechanisms that can be used to provide a circumferential fluid flowwhile still having a choice in the direction taken by the connector.

FIGS. 3 and 4 shows a second embodiment of the invention that is in mostrespects similar to the embodiment depicted in FIGS. 1 and 2. As shownin FIGS. 3 and 4, filtration unit 20 includes a circular frame 40 havinga lower annular edge seated on interior ledge 41, as in the FIG. 1arrangement. The upper annular edge 43 of frame 40 merges with anannular partition 63 that is constructed somewhat differently than thecorresponding partition in the FIG. 1 embodiment.

In cross section, partition 63 includes an arcuate upper section 65integrally connected to edge 43 of the filtration frame 40, and a mainsection 67 that angles downwardly away from the filtration unit to forma mounting rim 69. Vent ports 55 are formed in the arcuate upper section65, which is the highest point on partition 63.

As shown in FIG. 3, partition 63 causes the annular space 52 to have aninverted V cross section; the upwardly convergent nature of space 52causes any air bubbles to converge or concentrate near ports 55, therebypromoting a desired de-aeration of the swirling fluid in space 52. Thefiltration unit is mounted in the reservoir by means of rim 69 and theinterior ledge 41.

The FIG. 3 assembly functions in essentially the same fashion as theFIG. 1 construction. However, the cross-sectional configuration ofannular partition 63 is such that some fluid can accumulate in anannular space 71 surrounding the partition. To prevent long-termstagnation of fluid in space 71, the filtration unit can be providedwith a V-shaped passage (or groove) 73 that communicates space 71 withcentral space 47 within the filtration unit. The V-shaped passage wallbridges across partition 63 and the side wall of frame 40 to allow fluidto circulate from annular space 71 into central space 47. The exteriorsurface of the passage 73 wall slows the circumferential swirl in space52 near ports 55.

In major respects the FIG. 3 embodiment and the FIG. 1 embodimentoperate in the same fashion. It will be appreciated that some variationsin structure and arrangement can be employed while still practicing theinvention.

What is claimed:
 1. A reservoir for power steering fluid, comprising: anupright housing having a vertical axis said housing comprising upper andlower housing sections having mating annular edges joined together alongan interface; said upper housing section forming an upper interior spaceadapted to store a reserve supply of power steering fluid; said lowerhousing section comprising a stepped wall structure that includes afirst circular side wall extending downwardly from said interface, and asecond circular side wall located below said first side wall; saidsecond side wall having a smaller diameter than said first side wall sothat an annular ledge is formed at the juncture between said first andsecond circular side walls; a fluid inlet connection tangent to saidfirst circular side wall for directing fluid from a power steering unitinto said lower housing section; a fluid outlet connection tangent tosaid second circular side wall for directing fluid from the lowerhousing section to a pump that supplies fluid to the power steeringunit; and a filtration means seated on said annular ledge for removingcontaminants from the fluid flowing from said inlet connection to saidoutlet connection.
 2. The reservoir of claim 1, wherein said filtrationmeans comprises an upright hollow circular filtration unit having alower annular edge seated on said annular ledge, and an upper annularedge located within said upper housing section.
 3. The reservoir ofclaim 2, and further comprising an annular baffle means extending fromthe upper annular edge of said filtration unit for preventing fluidsurrounding the filtration unit from swirling upwardly into said upperinterior space.
 4. The reservoir of claim 1 wherein said housing has avertical height dimension and horizontal diameter dimension, saiddimensions being approximately the same.
 5. A reservoir for powersteering fluid, comprising: an upright housing having a vertical axis;said housing having an upper housing section defining an upper interiorspace adapted to store a reserve supply of fluid, and a lower housingsection having fluid connections with a power steering unit and a fluidpump, whereby the pump moves fluid from the power steering unit throughthe lower housing section and back into the pump; and a filtration meanslocated within said lower housing section for trapping solidcontaminants; said fluid connections being configured to direct thefluid circumferentially around said vertical axis while the fluid isflowing within the lower housing section: said lower housing sectioncomprising a first circular side wall (39) having a relatively largediameter, and a second circular side wall (42) having a relatively smalldiameter; said fluid connections comprising an inlet connection (50)tangent to said first circular side wall, and an outlet connectiontangent to said second circular side wall.
 6. The reservoir of claim 5,and further comprising a radial wall joining said first circular sidewall to said second circular side wall, whereby said lower housingsection has a stepped side wall construction: said filtration meanscomprising an upright hollow circular filtration unit concentric aroundsaid vertical axis.
 7. The reservoir of claim 6, and further comprisingan annular partition extending outwardly from said circular filtrationunit within said upper housing section for preventing flow from anannular space (52) surrounding said filtration unit into said upperinterior space; and plural vent ports (55) in said annular partition forventing air from said annular space into said upper interior space.